btrfs: change how repair action is passed to btrfs_repair_one_sector

There's a function pointer passed to btrfs_repair_one_sector that will
submit the right bio for repair. However there are only two callbacks,
for buffered and for direct IO. This can be simplified to a bool-based
switch and call either function, indirect calls in this case is an
unnecessary abstraction. This allows to remove the submit_bio_hook_t
typedef.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>